What Are Valid Data Blocks?

Valid data blocks are storage units that have been marked as occupied by the file system metadata in a file system (for example, EXT). These blocks contain actual data or file content. Unallocated blocks and unused blocks can be allocated by the system later, but usually do not contain valid data. During data migration, the system skips these unallocated or unused blocks and transmits only valid data in allocated blocks. This reduces the amount of data to be migrated and improves migration efficiency.

For details about block migration, see What Is Block-Level Migration?.